Date: Mon, 1 Mar 93 05:05:15 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V16 #237 To: Space Digest Readers Precedence: bulk Space Digest Mon, 1 Mar 93 Volume 16 : Issue 237 Today's Topics: Battery help needed! (2 msgs) Galileo Update - 02/25/93 Hopkins Leaks (was Re: Blimps) Mars CD-ROM products McElwaine disciplined! (somewhat long) Refueling in orbit (2 msgs) Sky & Telescope Weekly News Bulletin SOLAR gravity assist? Yup. (2 msgs) Soviet Energia: Available for Commercial Use? Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: 25 Feb 93 21:44:37 GMT From: "anthony.r.rizzo" Subject: Battery help needed! Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr In article <1mjbakINN781@gap.caltech.edu> bjmccall@cco.caltech.edu (Benjamin John McCall) writes: >Hi! > >I'm in charge of a student group at Caltech, and we're designing a small, >self-contained payload for the space shuttle to observe gamma-ray bursts. > >One major problem we've encountered is the battery pack - we need about 200 >Amp-hours of power (at about 0.5 Amps), but it has to weigh less than 100 >pounds. > >SLA (Sealed Lead-Acid) doesn't seem to have the energy density, and >Alkaline-Manganese (aka Duracell lantern batteries) have a very sloping >discharge curve, making them undesireable. NASA will not allow us to use >any kind of Lithium-based cells. > >Does anyone have any information on alternative battery technologies, or >even suggestions about who I might get in touch with (by phone or by email)? > >I've heard a little bit about Silver-Zinc, but have not been able to get in >touch with anyone who has any information. > >Any help is greatly appreciated - please reply by email, as I don't necessarily >read this newsgroup. > >Thanks in advance, > >Ben McCall >bjmccall@cco.caltech.edu > >-- >Ben McCall, Caltech - bjmccall@cco.caltech.edu >SEDS President, Technical Projects Coordinator You might consider using a fuel cell. NASA already uses a bunch of them on the shuttle. So safety should be less of a problem. A fuel cell also might have the appropriate energy density. All you'd have to do is provide the fuel cell with the appropriate supplies of O2 and H2, in the correct ratio of coarse. The output will be H2O + e. It's been a long time since I read about fuel cells, but I recall that 10 years ago there was considerable discussion about small fuel cells with solid polymer electrolytic membranes, i.e., no spillage of potentially toxic or corrosive liquids. I'm sure that NASA can give you more information on the subject. What do you think, RG? Tony Rizzo ------------------------------ Date: 26 Feb 93 02:03:39 GMT From: INNES MATTHEW Subject: Battery help needed! Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr In article <1mjbakINN781@gap.caltech.edu> bjmccall@cco.caltech.edu (Benjamin John McCall) writes: >Does anyone have any information on alternative battery technologies, or >even suggestions about who I might get in touch with (by phone or by email)? > >-- >Ben McCall, Caltech - bjmccall@cco.caltech.edu >SEDS President, Technical Projects Coordinator How about an aluminum-air battery? High-grade (>=99.99% Al) aluminum is the anode and some inert, porous metal used as a cathode, through which you bubble air. It's apparently a fairly high-energy-density cell, insofar as you get a great deal of electrical energy per kilogram (I don't have any sort of number,I'm afraid) and you get 2.7V per cell. All of this stolen out of my first-year Chemistry text. :-) Hope it's of some help. -- Matt Innes ------------------------------ Date: 25 Feb 1993 23:34 UT From: Ron Baalke Subject: Galileo Update - 02/25/93 Newsgroups: sci.space,sci.astro,alt.sci.planetary Forwarded from Neal Ausman, Galileo Mission Director GALILEO MISSION DIRECTOR STATUS REPORT POST-LAUNCH February 19 - 25, 1993 SPACECRAFT 1. On February 22, a NO-OP command was sent to reset the command loss timer to 240 hours, its planned value during this mission phase. 2. During the period from February 23 through February 24, a navigation cycle was performed. This navigation cycle provided near-continuous acquisition of two-way doppler and ranging data during four consecutive passes of the spacecraft over DSS-63 (Madrid 70 meter antenna), DSS-14 (Goldstone 70 meter antenna), DSS-42 (Canberra 34 meter antenna), and then back to DSS-63. 3. On February 24, real-time commands were sent to perform a Scan Actuator Subassembly (SAS) friction calibration to verify that the friction level has not changed; analysis of the data is in progress. 4. On February 25, a wobble angle identification (ID) activity was performed in the all-spin mode with the scan platform cone angle at 0 degrees and in the dual-spin mode with the scan platform cone angle at 153 degrees; analysis of the data is in progress. 5. On February 25, Delayed Action Commands (DACs) were sent to turn the Photometric Calibration Target (PCT) No. 1 heater on March 2 in accordance with the Retro-Propulsion Module (RPM) pressure profile strategy. 6. The AC/DC bus imbalance measurements have not exhibited significant change (greater than 25 DN) throughout this period. The AC measurement reads 19DN (4.3 volts). The DC measurement reads 141DN (16.6 volts). These measurements are consistent with the model developed by the AC/DC special anomaly team. 7. The Spacecraft status as of pin Configuration - Dual-Spin c) Spin Rate/Sensor - 3.15rpm/Star Scanner d) Spacecraft Attitude is approximately 7 degrees off-sun (leading) and 7 degrees off-earth (lagging) e) Downlink telemetry rate/antenna- 1200bps(coded)/LGA-1 f) General Thermal Control - all temperatures within acceptable range g) RPM Tank Pressures - all within acceptable range h) Orbiter Science- Instruments powered on are the PWS, EUV, UVS, EPD, MAG, HIC, and DDS i) Probe/RRH - powered off, temperatures within acceptable range j) CMD Loss Timer Setting - 240 hours Time To Initiation - 236 hours GDS (Ground Data Systems): 1. A review of the Phase 1 Telemetry Software Requirements Document (SRD) was completed on February 24th. No significant problems were identified. A final version incorporating comments received at the meeting will be published next week. Phase 1 capabilities support the new mission baseline through successful return of the Probe data and loading of the Phase 2 Flight Software for orbital operations in April 96. 2. Galileo participated in the DSN (Deep Space Network) Version 1.5 GCF (Ground Communications Facility) upgrade data flow test on February 24, 1993 from 19:00 to 01:00 GMT using DSS-10. The purpose of this test was to demonstrate telemetry data flow path through the DSN SFOC Gateway (SG) to the Error Correction and Switching (ECS) subsystem; the current data flow is the External User Gateway (EUG) to the ECS. This test exercised telemetry data for Galileo only. The test failed due to blocks of data being dropped between the SG and the ECS. The cause of this problem is unknown and is under investigation. A test report is expected from the DSN GCF cognizant engineer during the week of March 1. A retest of telemetry flow plus testing of command, monitor and tracking data flow through the SG to ECS interface will be performed prior to March 15, 1993. The Version 1.5 GCF upgrade is scheduled to be operational on March 15, 1993. 3. The IBM 3090/200 to IBM ES/9000 transition certification testing activities began on February 22. Initial testing by the Data Management Team (DMT) has uncovered job control default parameter differences between the two machines which require modifications to runstreams used by the DMT. Flight S/W certification testing is expected to begin during the week of March 1. Galileo certification testing activities will continue thru March/April 1993. Following successful completion of certification testing Galileo will transition from the current IBM 3090/200 to the new IBM ES/9000-6121/610. TRAJECTORY As of noon Thursday, February 25, 1993, the Galileo Spacecraft trajectory status was as follows: Distance from Earth 62,966,500 km (0.42 AU) Distance from Sun 210,819,800 km (1.41 AU) Heliocentric Speed 112,400 km per hour Distance from Jupiter 639,964,600 km Round Trip Light Time 07 min. 02 sec. SPECIAL TOPIC 1. As of February 25, 1993, a total of 65066 real-time commands have been transmitted to Galileo since Launch. Of these, 59961 were initiated in the sequence design process and 5105 initiated in the real-time command process. In the past week, 18 real time commands were transmitted: 3 were initiated in the sequence design process and 15 initiated in the real time command process. Major command activities included commands to reset the command loss timer, perform a Scan Actuator Subassembly (SAS) friction test, and a DAC to turn on the PCT No. 1 heater. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | If you don't stand for /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | something, you'll fall |_____|/ |_|/ |_____|/ | for anything. ------------------------------ Date: 25 Feb 93 14:10:26 GMT From: Bill Higgins-- Beam Jockey Subject: Hopkins Leaks (was Re: Blimps) Newsgroups: sci.space In article , jbh55289@uxa.cso.uiuc.edu (Josh Hopkins) writes: > A _dirigible_ is a steerable vehicle. It doesn't have to be rigid. Rigid > dirigibles are generally just called "rigids" (after you've established the > context) or occasionally zeppelins after Count Ferdinand von Zeppelin. If we're becoming *completely* pedantic, a "zeppelin" is a rigid dirigible airship built by the Count's method; there are other possible structures. Nearly all the rigid airships ever built were zeppelins (130 of them? Or was it 130 German ones and three American ones?) The British R100 and R101 are examples of non-zeppelin rigid airships. For the following paragraph we have the headline "Hopkins Leaks News of Balloon Project." (Or maybe it's just a trial balloon?) > Lighter than air vehicles do indeed have lots of potential for Mars, though the > difficulties can't be ignored. It is however _far_ easier than floating a > balloon on Jupiter, something Bill Higgins and I have been puttering around > with. Not much lately, though-- haven't had the time. Most weekends I can't even *get* to Jupiter... Oh, by the way (though this quest failed on sci.aeronautics last fall): We're looking for a textbook that details balloon design! Anybody know a good one? Moira Higgins on astronomy: Bill Higgins "I can always find Orion. Fermi National Accelerator Laboratory Besides that the Moon Internet: HIGGINS@FNAL.FNAL.GOV is my only other specialty." Bitnet: HIGGINS@FNAL.BITNET ------------------------------ Date: Thu, 25 Feb 1993 21:29:46 GMT From: Martin Connors Subject: Mars CD-ROM products Newsgroups: sci.space,sci.astro I got together this list for my own use by using NODIS at NSSDCA. Since interest may be stimulated by the Sky & Tel article and the fact that Mars Observer looks like a go I thought I would post it. I have no commercial interest in NSSDCA or the U.S. Government apart from a few promissary notes (with G. Washington's picture on them) in my dresser drawer. === CD-ROM products relevant to Mars Note that the MDIM is described in Sky & Telescope, March 1993, p. 94-96. The Space Science Sampler apparently has a number of images of Mars' moons. Summary: Space Science Sampler, Volumes 1 and 2 from the Planetary Data System (PDS). Two discs contain 800 images of Uranus, its rings and satellites, and 400 files of other space and Earth science data. Contact: Mr. Randal Davis LASP, Campus Box 392 University of Colorado Boulder, CO 80309 (303) 492-6867, Fax 492-5105 [] Mars Digital Image Model The Planetary Data System (PDS) at JPL, the Mars Observer project and the U.S. Geological Survey (USGS) has put together Mosaicked Digital Image Models (MIDM) of the Martian surface taken by the Viking Orbiter spacecraft. This CD-ROM set is not to be confused with the Viking Orbiter CD-ROM set released earlier. The Viking Orbiter CD-ROM contains raw Viking images only. The MIDM CD-ROMs are images compiled from the raw Viking images which were further processed to reduce radiometric and geometric distortions, and to form geodetically controlled mosaicked images. The data are stored as digital maps at 1/256 degree/pixel resolution (231 meters) and 1/64 degree/pixel resolution (943 meters). Also included are air-brushed maps of the entire planet of Mars at 1/16 degree/pixel resolution (3.69 km). Contact: NSSDC Coordinated Request and User Support Office Originator: Dr. Eric Eliason USGS Geological division 2255 North Gemini Drive Falgstaff, AZ 86001 (620)556-7113 ASTROG::EELIASON NSSDC ID 75-075A-01f/083A-01C QUANTITY 06 COST $50.00 + $9.00 (Software) + $2.50 (USA) or $10.00 (Overseas) Shipping/Handling SUGGESTED SOFTWARE IMDISP (DOS), or Image4PDS (Mac) NOTE [] The cost of the set is $50.00. You may request any subset or a combination of discs at a cost of $20.00 for first and $6.00 for each additional. [] Volume 7 is not yet available. [] Detailed information is listed below. (75-075A-01f) MDIM This data set contains a digital image map of Mars which is a cartographic extension of a previously released set of CD-ROM volumes containing individual Viking Orbiter Images (PDS data sets VO1/VO2-M-VIS-2-EDR-V2.0 (NSSDC IDs 75-075A-01c and 75-083A-01a) and VO1/VO2-M-VIS-2-EDR-BR-V2.0 (NSSDC IDs 75-075A-01d and 75-083A-01b)). The data in these earlier data sets are pristine, in that they were processed only to the extent required to view them as images. They contain the artifacts and the radiometric, geometric, and photometric characteristics of the raw data transmitted by the spacecraft. This new volume set, however, contains cartographic compilations made by processing the raw images to reduce radiometric and geometric distortions and to form geodetically controlled Mosaicked Digital Image Models (MDIMs). It contains digitized versions of an airbrushed map of Mars as well as a listing of all IAU-approved feature names. Special geodetic and photogrammetric processing has been performed to derive rasters of topographic data, or Digital Terrain Models (DTMs). Because the photometric processing used in this MDIM was over simplified, quantitative radiometric analysis on these data is not possible. The MDIM CD-ROM collection serves two purposes. First, the image collection serves as a data base for interactive map browser applications. Secondly, the CD-ROM volume set provides a dense delivery medium to build higher-derived cartographic image products such as special map series and planning charts for the Mars Observer Project. This set contains seven volumes. Volume 1 contains images of the Vastitas Borealis Region of Mars, 373 image files covering the entire north polar region of Mars southward from the pole to a latitude of 42.5 degrees North. Polar Stereographic projection images of the north pole area from 80 to 90 degrees are located in the POLAR directory on this disk. Volume 2 contains images of the Xanthe Terra Region of Mars, 412 image files covering the region of Mars from 47.5 degrees North latitude to 47.5 degrees South latitude, and 0 degrees longitude to 90 degrees West longitude. Volume 3 contains images of the Amazonis Planitia Region of Mars, 412 image files covering the region of Mars from 47.5 degrees North latitude to 47.5 degrees South latitude, and 90 degrees West longitude to 180 degrees West longitude. Volume 4 contains images of the Elysium Planitia Region of Mars, 412 image files covering the region of Mars from 47.5 degrees North latitude to 47.5 degrees South latitude, and 180 degrees West longitude to 270 degrees West longitude. Volume 5 contains images of the Arabia Terra Region of Mars, 412 image files covering the region of Mars from 47.5 degrees North latitude to 47.5 degrees South latitude, and 270 degrees West longitude to 0 degrees West longitude. Volume 6 contains images of the Planum Australe Region of Mars, 373 image files covering the entire South polar region of Mars northward from the pole to a latitude of 42.5 South latitude. Polar Stereographic projection images of the south pole area from 80 to 90 degrees are located in the POLAR directory on this disk. Volume 7 contains the Digital Topographic Map of Mars, MDIMs of the entire planet at 1/64, 1/16, DTMs of the entire planet at 1/64, 1/16, and the digitized airbrush map of Mars at 1/16 and 1/4 degrees/pixel. Each of the first six volumes contains MDIMs of the areas specified at resolutions of 1/256 degrees/pixel (231 m) and at 1/64 degrees/pixel (943 m). Volumes 1 and 6 also contain MDIM coverage of the entire planet at 1/16 degrees/pixel (3.69 km). Each of the six volumes also include a digitized airbrush map of the entire planet at 1/16 degrees/pixel (3.69 km) and at 1/4 degrees/pixel. The Sinusoidal Equal-Area Projection, is used as the map projection for this image collection. The tiling layout of the 1/64 degrees/pixel digital models is the same on the first six volumes. Note that the 1/64 degrees/pixel MDIM segments of which appear in Volumes 1 through 6, is duplicated in its entirety on Volume 7. All of the resolution compressions were done by averaging, not by subsampling. A gazetteer of IAU-approved feature names, referenced by latitude/longitude coordinates is included as a table file on each of the seven volumes. [] Viking Orbiter Images of Mars From the Planetary Data System (PDS). Eight image discs are available with compressed and browse images. More are scheduled to be available soon. Contact: NSSDC Coordinated Request and User Support Office Originator: Planetary Data System NASA/Jet Propulsion Laboratory Mail Stop 525-3610 4800 Oak Grove Drive Pasadena, CA 91109 (818) 306-6130 PDS_OPERATOR@JPLPDS.JPL.NASA.GOV NSSDC ID 75-075A-01c/d and 75-083A-01a/b QUANTITY 10 COST $74.00 + $9.00 (Software) + $2.50 (USA) or $10.00 (Overseas) Shipping and Handling SUGGESTED SOFTWARE IMDISP (DOS) or Image4PDS (Mac) NOTE [] The total cost of this set is $74.00. You may request any subset or a combination of discs at a cost of $20.00 for the first and $6.00 for each additional. [] There is no volume 9 for this set. [] Detailed information is listed below. Vol. Number Frame Numbers 1 122S01-166S24 2 167S01-210S42 3 211S01-251S30 4 252S01-321S72 5 319S12-363S56 6 365S01-405S30 7 406S11-436S36 8 437S01-467S36 10 003A01-038A32 11 039A01-070A32 See section on MDIM for the difference between Viking CD-ROM set the MDIM set. All volumes of the Viking contain both browse and compressed images. -- Martin Connors | Space Research | martin@space.ualberta.ca (403) 492-2526 University of Alberta | ------------------------------ Date: 25 Feb 93 18:50:03 GMT From: "Richard M. Warner" Subject: McElwaine disciplined! (somewhat long) Newsgroups: sci.skeptic,sci.space,sci.astro,sci.space.shuttle In article btd@iastate.edu (Benjamin T Dehner) writes: >Xref: sjsumcs sci.skeptic:25845 sci.space:24536 sci.astro:16739 sci.space.shuttle:4280 >Path: sjsumcs!octopus!pyramid!gossip.pyramid.com!olivea!charnel!rat!usc!wupost!crcnis1.unl.edu!moe.ksu.ksu.edu!hobbes.physics.uiowa.edu!news.iastate.edu!pv7440.vincent.iastate.edu!btd >From: btd@iastate.edu (Benjamin T Dehner) >Newsgroups: sci.skeptic,sci.space,sci.astro,sci.space.shuttle >Subject: Re: McElwaine disciplined! (somewhat long) >Message-ID: >Date: 24 Feb 93 16:43:52 GMT >References: >Sender: news@news.iastate.edu (USENET News System) >Organization: Iowa State University, Ames IA >Lines: 57 >In lord@tradent.wimsey.com (Jason Cooper) writes: > >>> Maybe it's about time a lot of these people learned about >>> a newsreader called 'nn'. > >>BRAVO! > >> Jason Cooper > > The issue here is not about content, but about volume. McElwaines >megalithic posted at frequent intervals take up network resources and disk >space wether or not I read them or kill them. Furthermore, it seems that >McElwaine himself never discussed his posts, but simply reposts and reposts >and reposts; in short, an automated pamphlet mailer, as someone else pointed >out. >Ben An additional orthogonal issue to the comments on bandwidth and disk space is that many folks pay $$$ for their news feeds, and long irrelevant posts are money down the drain (you cannot select before downloading). >--------------------------------------------------------------------------- -->Benjamin T. Dehner Dept. of Physics and Astronomy >btd@iastate.edu Iowa State University > Ames, IA 50011 >-- >----------------------------------------------------------------------------- >Benjamin T. Dehner Dept. of Physics and Astronomy >btd@iastate.edu Iowa State University > Ames, IA 50011 ------------------------------ Date: Thu, 25 Feb 1993 21:29:30 GMT From: Henry Spencer Subject: Refueling in orbit Newsgroups: sci.space In article <1993Feb25.154112.18992@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes: >>>>The Centaur which could have benefitted from on-orbit refueling >>>>never had a test program to achieve this mission... > >I was under the impression that Centaur has flown on unmanned launchers >many times since 1962... >... Certainly Titan IV can carry anything a Shuttle can into orbit. Not into the same orbit, it can't. That is exactly the issue here: Shuttle-Centaur has noticeably better performance than Titan-IV-Centaur. On-orbit fueling also opens additional possibilities, like stacking up more stages than will fit in a single launch now, e.g. *two* Centaurs or a Centaur with an IUS on top. The attempts to shoehorn a Mars sample return into Titan-IV-Centaur's capabilities produced some, uh, *interesting* mission plans... not ones that any sane planner would want to rely on. Nearly thirty years ago, we demonstrated the ability to mate a spacecraft to a separately-launched rocket stage in orbit, to give performance beyond what a single launch could provide. We're still not making any operational use of this capability, despite flying missions that really could use it. -- C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology effect since OS/360. | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Thu, 25 Feb 1993 23:22:48 GMT From: Dave Michelson Subject: Refueling in orbit Newsgroups: sci.space In article <1993Feb25.154112.18992@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes: > >I was under the impression that Centaur has flown on unmanned launchers >many times since 1962. Didn't both Vikings ride Centaurs without Shuttle >assist? Certainly Titan IV can carry anything a Shuttle can into orbit. >Why is Centaur a Shuttle only playload? If nothing else, this whole discussion underscores the need for rational long term planning for space science probes and solar system exploration. My hair practically stood on end while I read some parts of Bruce Murray's "Journey into Space". Centaur continues to evolve. AW&ST recently carried an item about General Dynamics looking for funding to develop a single engine version of the Centaur to increase both payload (marginally) and reliability. I guess price would also decrease slightly as well since it's easier to test and verify one engine than two. --- Dave Michelson University of British Columbia davem@ee.ubc.ca Antenna Laboratory ------------------------------ Date: 25 Feb 93 19:59:29 GMT From: Henry A Worth Subject: Sky & Telescope Weekly News Bulletin Newsgroups: sci.space In article <1993Feb22.221823.2692@news.arc.nasa.gov> bcollins@utdallas.edu (ARLIN B COLLINS) writes: > *** Please note S&T email addresses listed about the middle > *** of this text. > > SKY & TELESCOPE NEWS BULLETIN -- February 20, 1993 > > MORE HUBBLE WOES > The Hubble Space Telescope (HST) suffered its third gyroscope failure, > out of six on board, leaving the spacecraft's pointing-control system > without any backup. Earlier gyro shutdowns apparently occurred when > solder joints came unbonded. This latest failure occurred on November > 18th, but its cause was still unclear as of mid-February. Should > another gyro fail, HST would automatically stop observing and put > itself in a "safe mode." Furthermore, the current draw on one of the > remaining gyros increased for no apparent reason last summer and has > risen further since then. Space Shuttle astronauts will try to replace > as many as four gyros during the HST repair mission now scheduled for > December 1993. Details of this story appear in S&T's April issue, now > on press. Apologies in advance if this has been already thrashed to death, this group has so much volume its so easy to miss so much. Does the gyro-loss safe mode put Hubble into a slow stablization spin, or in the case of complete gyro loss does it become just a matter of time (and flapping solarpanels) until Hubble begins to tumble and has to be written off? How much lattitude does the repair mission have to safely repair a gyro-less Hubble, is the shuttle and arm even capable of coping with a slow spin, I don't recall there being a co-axial capture point (remember the difficulties with Solar Max, and the Hubble is so much bigger - one wrong move and they could lose a lot more than an astronaut - I'm still amazed that they took that risk)? Would they even be allowed to attempt approach and capture, even if the Hubble was still stable? -- Henry Worth No, I don't speak for Amdahl... I'm not even sure I speak for myself. ------------------------------ Date: 25 Feb 93 13:48:45 GMT From: Bill Higgins-- Beam Jockey Subject: SOLAR gravity assist? Yup. Newsgroups: sci.space,sci.astro,alt.sci.planetary This is long, but you'll like it, I promise. Recently on alt.sci.planetary I answered a post from a student who, I thought, had made an elementary error. >In article , ljensen@plains (Lars Jensen) writes: >> I am currently designing a space probe for flyby missions which will >> perform multi-purpose tasks to explore both Mercury and Pluto. > >"This is an ambitious young man," I thought. > >> one component staying in Mercury's orbit to map the Mercurian surface, >> while the other component travels with gravity-assistance of the sun to >> explore Pluto and Charon. > >*Bzzt* Wrong, but thank you for playing our game. Using the Sun for a >gravity assist is impossible. (You are welcome to try to convince me >otherwise.) [Note the hedging. Even when I am being arrogant I try to mitigate the risk of humiliation.] >In a gravity assist, you steal energy from the motion of >a planet around the Sun... in the planet's reference frame, you gain >no energy, but relative to the Sun you change your speed and direction >so you win. > >For moving around the Solar System, this trick is not possible using >the Sun. > >If you want to send a spacecraft to Pluto, you will have to do it by >more conventional means (like gravity assist from mere gas giants). I went on to answer his request for information about Pluto, to prove I was really not such a nasty guy. Shortly, I received e-mail from Dr. Bill Cochran of the University of Texas. He pointed out that all objects in the solar system orbit around the "barycenter," the center of mass. This point is *not* (usually) inside the surface of the Sun! I replied (with a copy to Lars Jensen): >Wow, this is certainly astonishing. This will teach me to make arrogant >pronouncements to undergraduates... > >Assuming Jupiter is the only planet, and it's in a circular orbit, I >get a distance of 7.43E10 cm between the barycenter and the Sun's >center of mass, and the solar radius is 6.9599E10 cm in the book I >looked in (which insists on cgs units). This is only 93.7% of the >distance to the barycenter, a good 47,000 km from the edge of the Sun. >(But where is the edge? Suddenly the uncertainty in solar radius >measruments becomes interesting, and my handbook-- Zombeck's *Handbook >of Space Astronomy and Astrophysics*-- is silent.) [Bill noted in reply that my figure is correct for the equatorial solar radius.] >Continuing these assumptions, the Sun would describe a circle around >the barycenter once per Jovian year, covering (two pi R) 292,700 km >in 4332.589 days, or 67.56 km per day, 78.2 centimeters per second. >Hmm. Jogging speed. [Then we discussed Lars's hypothetical gravity-assist maneuver.] >Good puzzle. Want to tackle it? Can our friend in North Dakota >actually pick up useful speed, provided his Pluto probe passes closer >than 47,000 km to the Sun? What's the upper limit on the delta-V you >can get this way? And is the performance increase mitigated by the >amount of suntan oil you have to bring along? > >I'm not familiar with making gravity-assist calculations. Maybe >somebody on the Net will have a textbook with formulas... Bill is a specialist in looking for planets in other solar systems by the perturbing effects they have on their stars. No wonder he knew that the barycenter is (often) outside the Sun! So I'm posting this not only for everybody's amusement, but to take it further. What is the maximum delta-V available from a solar gravity assist in a Sun-Jupiter solar system, assuming your probe can skim the surface of the Sun? There must be somebody out there taking astrodynamics this term, or even *teaching* it. (If so, I've just given you an exam problem.) Or maybe it's a good coffee-machine problem around JPL or Lewis or some astronomy department... Extra credit questions: 1. If the answer is usefully large, can you follow a solar slingshot with a Jovian slingshot and get even more energy? Can you somehow repeat this trick for endless energy pumping, or show that this is impossible? 2. How much help do you get when you throw in Saturn? Rs= 1.427E9 km, Ms= 5.688E26 kg, Msun=3498.5 Msaturn. 3. [Library question:] What is the uncertainty in the solar radius? What is the density profile of the solar atmosphere? How did people measure these things? 4. How *do* you engineer a spacecraft to go arbitrarily close to the Sun? (Spare me Brin's "refrigerator laser," I already know about it and his ship uses magic technology for its other systems.) 5. (We're beginning to get into thesis material here) The extent of the solar atmosphere must limit you somehow, even if your probe can stand the near-Sun radiation environment indefinitely. How do you solve the problem for a non-negligible solar atmosphere? All right, I know we don't have materials that will stand 5800 K, let alone the frictional heating you'd get at speeds where you're practically fall into the Sun. But suppose the probe is a big comet that just happens to fall in along the right path, and it survives to emerge as a little comet. What is its optimal path if you take helioaerodynamics into account? I *told* you this was going to be fun. Bill Higgins, Beam Jockey | Here Lies Bill Higgins: Fermi National Accelerator Laboratory | He Never Ever Learned Bitnet: HIGGINS@FNAL.BITNET | To Play Guitar So Well Internet: HIGGINS@FNAL.FNAL.GOV | But He Could Read and Write SPAN/Hepnet: 43011::HIGGINS | Just Like Ringing A Bell ------------------------------ Date: 26 Feb 93 02:31:27 GMT From: Paul Dietz Subject: SOLAR gravity assist? Yup. Newsgroups: sci.space Bill Higgins asks about a "solar gravity assist". This is *not* the same as the more well-known Jupiter gravity assist. Rather, it is an example of the Oberth Effect -- rockets are more effective when fired deep in a gravity well. Imagine the following occurs. A spacecraft falls from infinity along a near-parabolic orbit towards the sun. At perihelion, it is moving at (say) 200 km/s. It fires its rocket, adding 4 km/s to its velocity. It is now travelling at 204 km/s. How fast will it be going at infinity? Answer, from conservation of energy: sqrt((204)^2 - (200)^2) = 40.2 km/s! Viewed another way: the spacecraft moved a long distance while the rocket was firing at perihelion, so the work done on the spacecraft (force x distance) was large. Where did this extra energy come from? The reaction mass expelled by the spacecraft is now in a more tightly bound orbit. The gravitational potential energy liberated has been given to the spacecraft as kinetic energy. So, I really lied: this *is* a little like the Jupiter gravity assist, except that instead of bouncing the spacecraft off Jupiter, we're bouncing it off the reaction mass. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Thu, 25 Feb 1993 22:24:59 GMT From: "Garret W. Gengler" Subject: Soviet Energia: Available for Commercial Use? Newsgroups: sci.space Can anyone tell me if the Soviets are still offering their launch vehicles, specifically the Energia, for commercial use? I'm having trouble finding any information that is at all recent. The latest info I have is from an article in the Washington Post, February 22, 1992, when the head of NPO Energia "invited US officials to consider buying or leasing (the Energia) ..." I'm involved in a spacecraft design course here at the U of I and the launch requirements are tremendous. Any recent information on the Energia would be very helpful. Please respond via email to g-gengler@uiuc, since I don't read this group. Thank you for your time. Garret Gengler g-gengler@uiuc.edu ------------------------------ End of Space Digest Volume 16 : Issue 237 ------------------------------